O. Beckman

First Order Magnetic Phase Transition in Fe2P

The magnetic properties of stoichiometric Fe2P and non-stoichiometric Fe2-xP (0 < × ≤ 0.06) have been studied by means of magnetic susceptibility. Measurements on pure stoichiometric Fe2P samples show that there is a first order magnetic phase transition from a ferro- to a paramagnetic state at 216 ± 1 K. The transition is accompanied by a discontinuous change in the dimensions of the hexagonal unit cell with a decrease in the a-axis of 0.06% and an increase in the c-axis of 0.08% for increasing temperature. The transition is interpreted to be of magnetoelastic origin with an exchange energy critically sensitive to the interatomic spacing. Measurements on single crystals show that the spins are directed along the hexagonal c-axis with an exceedingly high axial anisotropy. The saturation moment is 1.46 μB/iron atom and the anisotropy energy as estimated from low field data is ~ 2.5 × 106 J m-3 (2.5 × 107 erg cm-3). The transition behaviour is very sensitive to the magnitude of the external field as well as to the presence of impurities and deviations from the ideal stoichiometry in the samples.

Elastic Constants of Aluminum

The adiabatic elastic constants of aluminum have been measured with an ultrasonic pulse technique at liquid‐heluim, liquid‐nitrogen, and room temperatures. The values of the elastic constants at 4°K are c11=11.63, c12=6.48, and c44=3.09 in units of 1010 N/m2. The Debye characteristic temperature calculated from these figures is θ=425°K in good agreement with the value obtained from speciffic heat data.The shear elastic constants ½(c11−c12) and c44 are discussed with reference to the theory given by Leigh.

The anomalous magnetisation of amorphous metglas 2826-A

Abstract Magnetisation measurements made on the amorphous ferromagnet Metglas 2826-A, (TC = 254.5 K), in the temperature range 4.2 ≤ T ≤ 450 K indicate that it obeys the static scaling law hypothesis over an unusually wide temperature range. Analysis of the data give for the critical exponents δ = 5.07, β = 0.41, γ = 1.67. Moreover, above TC a superparamagnetic model is discussed.

Towards equilibrium in spin glasses (invited)

New nonequilibrium features of the magnetic susceptibility of spin glasses are reviewed. Experimental observations on the time variation of the zero‐field‐cooled (ZFC) and field‐cooled (FC) susceptibilities indicate that the same equilibrium value is obtained after the same characteristic time teq(T). ZFC and ac susceptibility measurements on metallic spin glasses unambiguously reveal the existence of aging of the zero‐field spin‐glass state. The possibility to probe the aging process from these measurements is outlined. The aging of the zero‐field state ends at the characteristic time teq(T), where a spin‐glass state at dynamic equilibrium is retained.

Doping properties of Sb2Te3 indicating a two valence band model

Abstract Seebeck coefficient and electrical conductivity has been measured on Sb2Te3 doped with Pb, I, CuBr2, Sn etc. The material is always strongly p-type with S ≅ 80 μV⧸°K and σ varying between 2.105 and 5.105(Ωμ)−1. The S versus σ curve indicates two valence bands with parameters μ 0 ( m ∗ m ) 3 2 = 0.0057 m 2 /V s and 0.034 m2⧸Vs separated by 0.23 eV. The doping behaviour i discussed in terms of the crystal bonding.

Elastic Constants of CsBr and CsI from 4.2°K to Room Temperature

The elastic constants of pure single crystals of CsBr and CsI have been measured at liquid‐helium, liquid‐nitrogen, and room temperatures. For CsBr, the values of c11, c12, and c44 at 4.2°K are 3.437, 1.035, and 0.999 in units of 1010 N/m2. The corresponding values of CsI at 4.2°K are 2.737, 0.793, and 0.825·1010 N/m2.The elastic constants give the Debye temperature 148.8°K for CsBr and 125.6°K for CsI.The infrared resonance frequencies calculated from compressibility data are in agreement with those obtained from infrared spectroscopy.

Anomalous time dependence of the susceptibility in a Cu(Mn) spin glass

Abstract Complex ac susceptibility as well as field cooled dc magnetization measurements have been performed in a SQUID magnetometer on a Cu(4 at% Mn) spin glass. In all these measurements a step change in temperature gives rise to significant relaxation effects, which persist for a considerable time well after that thermal equilibrium is reached.

Specific heat and magnetic susceptibility of single phase YBa2Cu3O7

Abstract The specific heat of a single phase sample of the high T c superconductor YBa 2 Cu 3 O 7 has been measured. The specific heat jump at T c (91.6 K) is found to be ΔC e / T c =59 mJ / mol K 2 , which is considerably larger than previously reported values. From low field magnetization measurements the width of the transition of our sample is found to be 0.4 K.

Helical Spin Arrangement in Cubic FeGe

The magnetic properties of single crystals of the cubic B20 modification of the metallic compound FeGe have been investigated by means of a vibrating-sample magnetometer and a torsion balance. Transition to an ordered spin structure occurs at 280 K. Magnetization curves below this temperature shown an almost linear field dependence for the [100], [111] directions with a field of about 2 kOe required for saturation at low temperatures, indicating a small magnetocrystalline energy compared to the exchange energy. The saturation moment as extrapolated to zero Kelvin corresponds to 1.0μB. A model with the spins forming a helical screw propagating in the [111] direction at zero field is proposed to explain the observed magnetic properties.

SQUID Magnetometer for Mangetization Measurements

A magnetometer using a symmetric rf-biased SQUID (Superconducting quantum interference device) is described. The instrument has been designed for magnetization measurements of small single crystals at low magnetic fields in the temperature range 4.2-400 K. At low temperatures the sensitivity in magnetic moments is 2 × 10-12 Am2 or 2 × 10-9 emu, which is equivalent to Δχ = 10-7 SI with sample volume 3 mm3 at 0.01 T (100 Oe).